Microwave absorption memory system



June 1969 R. GAMBLIN ETAL 3, 0

MICROWAVE ABSORPTION MEMORY SYSTEM Filed Oct. 22. 1965 MCROWAE 2\8 10 o CILLA 0 %IIWEZC% 1 INVENTORS RODGER L. GAMBLIN PHILIP -A. LORD ATTORNEY United States Patent MICROWAVE ABSORPTION MEMORY SYSTEM Rodger L. Gamblin and Philip A. Lord, Vestal, N.Y., as-

signors to International Business Machines Corporation, Armonk, N.Y., a corporation of New York Filed Oct. 22, 1965, Ser. No. 502,008 Int. Cl. Gllb 5/64; H01f 7/00; H03f 9/00 U.S. Cl. 340-174 6 Claims ABSTRACT OF THE DISCLOSURE A microwave absorption and non-destructive memory system in which a ferrite element operating at its gyromagnetic resonant frequency presents a high or a low loss of microwave energy depending on the magnetic state of the ferrite element. In a first stable state, the ferrite element absorbs microwave energy. In a second stable state, the ferrite element does not absorb microwave energy. The ferrite elements are interrogated by means of a helical waveguide structure which is energized at one end by means of a microwave source and has the other end connected to a sense amplifier for determining the amount of microwave energy transmitted through the ferrite element.

The present invention relates to memory systems and, more particularly, to a non-destructive readout memory system operating according to the principle of gyromagnetic resonant absorption.

Ferrite cores have long been the standard element employed as a means for storing a single memory bit. Generally the readout time of the information held by the magnetic core is limited by the switching time of the material which makes up the core. Efforts have been made to increase this switching rate by changing the physical dimension of the core additionally, cylindrically shaped magnetic film storage elements have been tried to increase the switching rate. The thin walls of these cylindrically shaped magnetic films give improved switching time characteristic over the standard ferrite core at the expense, however, of problems with low level signals and/ or ditficulties of making proper wiring arrangements. Even this increased switching time of cylindrically shaped film also leaves room for improvement. The present invention supplies an improved memory system having a readout time of less than 50 nanoseconds. This readout is of a non-destructive nature and is of the type which can be repetitively recycled without damage to the contents of the storage element.

It is an object of the instant invention to provide an improved memory system having a reduced readout time.

It is a further object of the instant invention to provide a memory system operating in the non-destructive readout mode.

It is a further object of the instant invention to provide an improved storage element employing a helical waveguide structure as a means of generating a highly circular polarized microwave signal.

It is a further object of the instant invention to provide an improved memory system employing a ferrite core as a storage element, a helical wave structure as a means for generating a highly circular polarized magnetic field for non-destructively sampling the status of the storage element wherein, the nondestructive readout operation is made possibly by the energy coupling between the highly circular polarized magnetic field and the precessing electrons in the ferrite material of the core.

It is another object of the instant invention to provide an improved memory system operating in the non-destructive readout mode and employing a circularly polarized microwave signal as a means for sampling the status of a storage element.

It is a further object of the instant invention to provide an improved memory system wherein the status of the storage element is sampled by passing microwave energy sufliciently near a ferrite storage element whereby one state of this storage element is identified by the absorption of microwave energy from an associated highly circular polarized magnetic field by the precessing electrons in the magnetized storage element and the other state of the storage element is identified by the non-absorption 0f the microwave energy by the precessing electrons in the magnetized storage element because the sense of rotation between the electrons and the magnetic field are opposite. The absorption and non-absorption is determined by an associated sense amplifier.

These and other objects of the instant invention are realized by a novel combination of elements providing an improved memory system comprising a tunnel diode or Gunn elfect oscillator as a source of microwave energy, a helical waveguide structure, connected at one end to the source of microwave energy, as a means for generating a highly circular polarized magnetic field, a sense amplifier connected to the remaining end of the helical wave structure as a means of determining the presence of microwave energy on the helix, and a ferrite core as a storage element. Additionally, the gyromagnetic resonant frequency of the ferrite core is substantially matched to the frequency of the microwave source so that the status of the ferrite core can be non-destructively sampled by passing microwave energy in close proximity to the core. A first status, representing a binary one, of the magnetic core absorbs the microwave energy passing nearby. A second status, representing a binary zero, is sampled by passing the microwave energy from the microwave source to the sense amplifier substantially undiminished.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings; wherein:

FIG. 1 is a general block diagram of the instant instant invention;

FIG. 2 is the standard magnetization curve of magnetic oxide material;

FIG. 3 is an isometric view of a pair of coil-core storage elements with two sections showing the strip lines connected therewith;

FIG. 4 is a schematic diagram of the selection scheme used to turn on one of the microwave sources employed in the invention; and

FIG. 5 shows a sense amplifier suitable for use in the instant invention.

The same numerals are used in the several views to identify the same element.

Resonant absorption characteristics in ferrite material positioned within a magnetic field were early noted by A. G. Fox et al. in their article entitled Behavior and Application of Ferrite in the Microwave Region published in the Bell Systems Technical Journal, volume 34, pages 5-103, January 1965, especially pages 10-12, and 61-65. The authors therein recognized the resonant absorption of microwave energy by a solid ferrite slug positioned in a waveguide, which slug was subjected to an externally generated magnetic field of high intensity. The microwave energy was suitably absorbed in both directions at the same rate when the magnetic material was placed in the center of a waveguide.

The use of magnetized ferrite rings as an isolator for a helical transmission line is described by B. N. Enander in the Proceedings of the IRE, October 1956, page 1421 3 in an article entitled A New Ferrite -Isolator. The ferrite isolator described in this article is suitable for use in a traveling wave tube to reduce oscillations within the tube.

S. -E. Webber et al. describes in United States Patent 2,900,557 the use of ferrite material as an absorbing agent when exposed to an externally generated magnetic field. The ferrite material is employed to reduce oscillation within a traveling wave tube.

T. A. Kriz et a1. describes a ferrite storage system emplying microwaves in their article entitled Microwaves in their article entitled Microwave Readout of Ferrite Memory Storage in the February 1965 IEEE Transaction of Electronic Computers at page 75.

The foregoing articles, among others, relate to various aspects of the gyromatic resonant absorption characteristic of ferrite material. These articles do not show a nondestructive read only memory system based upon the principle of gyromagnetic resonant absorption as disclosed in FIG. 1, which is a block diagram of the present invention including a plurality of ferrite toroids 1a, lb, and 1c. The term ferrite is used to refer to that class of magnetic metals which possess extremely high resistivity and tensor permeability whereby, in combination, the class exhibits a gyromagnetic resonant absorption effect. The term toroids is used to describe that group of geometric shapes which can be circularly magnetized. An essential element of circular magnetization is a toroid having an inner wall 2 forming a bore 3 which acts as an air gap for preventing non-azimuthal magnetization. The bore 3 need not be a central bore lying on the axis of its associated toroid and the toroid need not have the shape of a cylindrical core. For example, an askew bore in a non-cylindrical toroid would give satisfactory results. However, a cylindrical toroid with an axial bore is shown since their use results in the best embodiment presently known. Each of the cores 1 is responsive to a partial current switching network 4 comprising, for example, a horizontal wire 5 and a plurality of vertical wires 6, 8 and 10. The switching network 4 follows standard techniques to circularly magnetize each of the cores to either of its two saturated states shown as 12 and 14 in FIG. 2. When the switching current is removed, the magnetic state of the core moves from its saturated condition 12 and 14 to its stable quiescent positions 16 and 18 respectively. Position 12 and 16 represent the saturated and quiescent position associated respectively with a binary one, and positions 14 and 18 represent the saturated and quiescent position associtaed respectively with a binary zero.

When the core 1 is magnetized in one direction, for example position 16 on the BH curve, one electron in the ferrite material finds itself in the field of all the other electrons. The one electron is not free to move alone in response to an external magnetic fieldbecause of exchange interactions, but rather must respond to the external magnetic field together with its neighboring electrons. Because an electron has both a magnetic moment and angular momentum, it acts lake a small magnetized top when exposed to an external magnetic field. When the electron is in this external magnetic field, the field attempts to rotate the electron so that the two become aligned. Like all tops upon which such forces act, however, the electron does not line up with the field, but instead precesses or swings about the field direction. With a magnetic field which is rotating in the same sense as the electron precesses, the electron absorbs energy from the field and tends to become disaligned therefrom. This process of the precessing electron tending to absorb energy from an external field is generally known as gyromagnetic resonant absorption.

In the case of isolated electrons the magnetization state can be disaligned from a steady field by means of the circularly polarized field. In a ferrite however, the individual electrons are coupled together so that actual disalignment from the DC magnetic field in which the electron finds itself does not occur, but rather the rotating magnetic field is absorbed by the ferrite and converted to heat.

A microwave oscillator 20, shown in FIG. 1, generates a microwave signal having a frequency substantially equal to the gyromagnetic resonant frequency of the ferrite material which comprises the core 1. A strip line 22 carries the microwave signal from the oscillator 20 to a plurality of helices 24, 26 and 28. A tapered strip line and mismatching elements, not shown, direct an equal amount of microwave energy to each helix. The microwave signal traveling along the helix 24 generates a rotating magnetic field in a plane which contains the axis of the helix. More specifically, the rotating magnetic field becomes highly circularly polarized in a single direction from the physical characteristics of the helix. More specifically, the helix 24 shown in FIG. 3 is a left-wound helix and generates a left-circular polarized wave with substantially no right circular component. This rotating field has a particular sense so that when the electrons in the ferrite core 1 surrounding the helix 24 are precessing within the field in the same sense they will couple strongly to the field. This coupling causes a strong attenuation of the microwave signal called gyromagnetic resonant absorption. The preceding description applies to the combination having a core I switched to its first state 16 of remnant magnetization. If the electrons in the magnetic core 1a are rotating in the opposite sense, that is the core is in the opposite remnant state 18, no such coupling or resonant absorption will occur.

The microwave energy passing through the core 1a is transferred to a second strip line 30a, by a direction coupler 32a. The strip line 30a termintes in a sense amplifier 34a. The remaining cores 1b and 1c are similarly equipped with couplers 32b and 320 and sense amplifiers 34b and 34c respectively.

The helical winding 24 need not necessarily be restricted to any one particular spatial relationship to its respective core 1a. The relationship shown in FIG. 3 places the helix 24 within the coil 1a and immediately adjacent the inner wall 2 of the core 1a. Although this spatial relationship shown provides a useful device suitable for employment with high speed data processors, an improved relationship is shown in a copending application Ferriresonant Memory System, SN. 500,941, and assigned to the assignee of the present invention. An additional possible spatial relationship, not shown, places the helix alongside an outer wall 36, FIG. 3, of the core making the center lines of both the core 1a and the helix 24parallel. The ferrite material employed may assume various geometric shapes. One of which is that the bore may be located off-center of the core. All the described spatial relationships have a single factor in common, that is, the electrons in the magnetized ferrite core in one stable state are rotating in the same sense as the electrons in the mangetic field of the highly circular polarized microwave signal causing gyromagnetic resonant absorption. No coupling results when the core is in its other stable state and the microwave signal passes through the core. The various geometric changes only cause a variation in the energy ratio of the microwave signal passing through the core for the two states of the magnetic core.

Referring again to FIG. 3, the strip line 22 is equipped with a ground return plane 38 which extends parallel to the strip line 22 but separated therefrom by a dielectric barrier 40. The strip lines 30:: and 3017 are equipped with a similarly positioned ground return plane which is not shown for purposes of clarity since this ground plane, if shown, would completely conceal the strip lines 30a and 30b.

Referring to FIG. 4, a half select circuit 42 is shown as a representative partial current switching circuit for the microwave oscillator 20 shown in FIG. 1. The microwave oscillator employed in the present invention is a Gunn effect oscillator 43 completely described in U.S. Patent 3,365,583 assigned to the assignee of the present invention. A first resistor 44 is connected to a first select line 46, and a second resistor 48 is connected to a second select line 50. The other end of the resistors 46 and 48 are connected together and to an excitation line 52 and a third resistor 54. The other end of the resistor 54 is connected to ground 56. The half select voltages from the select lines 46 and 50 combine in the resistor 54. The excitation voltage is applied to the Gunn effect oscillator 43 by the excitation line 52. When excited, the Gunn effect oscillator produces a microwave signal which travels down the strip line 22.

Referring to FIG. 5, there can be seen a schematic diagram of a sense amplifier 34 suitable for use with the instant invention. The amplifier is of standard design except that it responds to the rectified microwave signal. A microwave diode 58 and a resistor 60 are connected across the strip lines 22 and 38 to rectify the microwave signal. In accord with standard practice, tuning stubs, not shown, can be attached to strip line 22 to insure impedance matching between the strip line 22 and the diode 58. In addition other types of amplifier can be used; for example, transistor 61 can be tunnel diode to maximize the gain of the signal from diode 58, or other connections can be used for transistor 61 such as a grounded base connection which at the cost of speed would maximize power gain.

Referring again to FIG. 1, there can be seen an illustrative memory constructed according to the principles of the instant invention. In the illustration, a three-bit word is shown, that is, each of the cores 1a, 1b and stores one bit of information. It has been found that as many as seventy-two bit positions operate satisfactorily with a single oscillator 20. More specifiically, the micro wave energy generated by the Gunn effect oscillator is equally divided between all the memory elements attached to the line 22. A certain minimum power limit is required to produce a sufficient signal to noise ratio in order to distinguish between the presence and absence of the microwave energy at the sense amplifiers 34. It has been found that a representative oscillator develops 100 milliwatts of energy and if 1000 microwatts of energy is channeled into each helix an acceptable signal to noise ratio of 10 db is developed at the sense amplifiers 34 to determine the absorption and non-absorption states of the cores 1.

A plurality of microwave oscillators with associated magnetic cores as shown in FIG. 1 can be combined to construct a non-destructive read memory. A single oscillator is supplied for each group of cores 1. The group of cores 1 stores one word in the memory. Corresponding cores in adjacent words are connected to a single sense amplifier by additional direction couplers 32 and the strip lines 30 shown in FIG. 1. Generally, then a single oscillator is employed to furnish microwave energy to a single word comprising a plurality of microwave absorption storage elements. Each word is of uniform length and one group of sense amplifiers are employed to determine the status of corresponding cores in each word. It is easily understood how a single group of sense amplifiers can be employed in this manner since only one microwave oscillator is turned on at one time by the selection scheme shown in FIG. 4.

Some advantages, among others, of a memory constructed according to the principles of the present inven tion are that each memory element is non-destructively sampled by microwave energy and an increased read-out rate. More specifically, an associated sense amplifier will detect microwave energy when the core is in one resonant state of remnant magnetization and will not sense microwave energy when the core is in its second state of remnant magnetization. A 20 db signal difference has been obtained at the sense amplifier to identify the two remnant states. Also, the speed of the read-out operation depends only upon capability of the microwave circuitry to respond to the remnant state of the core. This response takes only a few cycles of the microwaves and thus is capable of operation in the nanosecond or less than nanosecond time period. The turn-on time of the associated oscillator 20 and the response time of the associated sense amplifier 34 increased the read-out time to approximately 50 nanoseconds.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A microwave absorption memory system comprisa plurality of ferrite elements each having a bore positioned therethrough,

said elements having a gyromagnetic resonant absorption frequency,

first means for individually magnetizing said ferrite elements to a first stable state of remnant magnetization or to a second stable state of remnant magnetization,

said magnetized ferrite elements having electrons with a first sense of rotation corresponding to said first stable state of remnant magnetization and having electrons with a second sense of rotation corresponding to said second stable state of remnant magnetization,

a source of microwave signals operating at substantially said resonant absorption frequency,

a plurality of second means individually positioned adjacent said elements and connected to said source for circularly polarizing said microwave signals in said first sense of rotation,

said ferrite elements in said first state absorbing said microwave signals and said ferrite elements in said second state passing said microwave signals undiminished thereby, and

sense amplifier means connected to said second means and responsive to said microwave signals for providing an output signal indicating the state of remnant magnetization.

2. A microwave absorption memory system as recited in claim 1 wherein said source of microwave signal is a Gunn effect oscillator.

3. A microwave absorption memory system as recited in claim 1 wherein said bore is axially located in said ferrite element.

4. A microwave absorption memory system as recited in claim 1 wherein said second means is a helical coil.

5. A microwave absorption memory system as recited in claim 4 wherein said helical coil is positioned within the bore of said element.

6. The microwave absorption memory system comprismg,

a plurality of cylindrically shaped ferrite elements arranged in associated groups,

each of said elements having a substantially common gyromagnetic resonant absorption frequency,

first means for selectively magnetizing each of said ferrite elements to a first stable state of remnant magnetization and to a second stable state of remnant magnetization,

a source of microwave signals connected to each group of said elements and operating at substantially said resonant absorption frequency,

each of said magnetized elements being formed with a bore lying in a plane perpendicular to the magnetic field generated by the magnetization of said ferrite element,

each of said elements having electrons in a first sense of rotation corresponding to said first stable state of remnant magnetization and having electrons in a second sense of rotation corresponding to said stable state of remnant magnetization,

a plurality of helical coils,

one of said coils being positioned in the bore of each element and connected to its corresponding source of microwave signals for generating a magnetic field having substantially one sense of rotation,

said element in said first state absorbing said microwave signals and said element in said second state passing said microwave signals undiminished there through,

second means for selectively energizing one of said microwave signal sources, and

third means connected in common with correspond- 15 -ing coils in each of said groups to determine the absorption of said microwave signals and the passing of said microwave signals in corresponding elements.

References Cited UNITED STATES PATENTS 2,911,55'4 11/1959 Kompfner et a1. 333-24 XR 3,155,941 11/1964 Mims 340-173 Storage, IEEE Transaction on Electronic Computers, February 1965, pp. 75-76.

BERNARD KONICK, Primary Examiner.

G. M. HOFFMAN, Assistant Examiner.

U.S. Cl. X.R. 

